In one mode of the manufacture of photographic film, very long webs of a suitable support are coated with light sensitive emulsion layers and dried. The coated webs are then slit into a plurality of narrower strips, which are spooled and segmented into a plurality of film packages, e.g. film roll cartridges or cassettes. It is useful for quality control and other purposes to have data about the film, (e.g., manufacture identity, film emulsion type, roll frame numbers, etc.) printed on the film with alpha numeric characters or other data symbols, such as bar codes, all collectively referred to herein as "data characters". One convenient way to record particular film data is to expose the edges of the film that will not subsequently be used for picture images, with patterns of radiation (e.g. light) to which the film emulsions are image-wise sensitive. Thus, latent images of data character patterns are recorded along the film edge(s) and will be developed subsequently, after the picture areas are exposed by the camera user and processed by the photofinisher. Such data is helpful during subsequent photofinishing operations, e.g., for adjusting print exposures and identifying particular image frames.
One approach for recording such film edge data characters has been to provide stencil belts having light transmissive data characters portions that constitute the information to be recorded. The belts are located along the film-strip spooling path and moved in synchronism with the film-strip material, so that light directed toward the film through the belts transmissive portions will record the belt's data pattern repeatedly onto successive edge sections of the photographic film strip. This approach operates successfully; however, it has disadvantages. For example, new belts must be fabricated and installed in the spooler system whenever different film data is desired. Also, the rapid velocity of the film strips require correspondingly rapid velocity along the belt recirculation path, which makes a long belt life difficult to achieve.
U.S. Pat. Nos. 4,519,701 and 4,553,833 describe an electro-optic approach wherein light emitting diode (LED) arrays are selectively activated and imaged onto an edge region to record data on film strip media moving through a spooling system. These systems present problems in regard to the attainment of adequate light intensity to adequately record on the rapidly moving film edge; and complicated exposure control electronics and/or imaging optics are employed to achieve adequate exposure intensity. When arrays having a large number of such LED elements are used, the problem of addressing the arrays energizing circuitry to form different data characters becomes difficult. This addressing difficulty increases significantly as the rates of address (changing from one set of characters to others) increases. Since the high film velocity in spoolers necessitates high address rates, the use of LED arrays as described above leaves room for significant improvements. Also, printing with LED arrays requires continuous and very accurate tracking of the film position in order to coordinate the many, successive small portions of image exposure and make the overall image appear continuous. The high film velocity in spoolers presents image-quality difficulties for the LED approach.
Other electro-optic printer systems such as laser writers and cathode ray tube devices have been considered (see the Background discussion in the above cited '701 patent); however, the cost, complexity and difficulty in integrating such devices to image on rapidly moving film strip edges, motivates against the use of these devices.
Another class of electro-optic light writing devices utilizes light valve modulator assemblies (e.g. PLZT or LCD panels with pixel addressing electrode systems and sandwiching light polarizer and analyzer plates) to patternwise control the passage of a uniform light illumination beam that is directed to a print zone. U.S. Pat. No. 4,050,814 is exemplary of one such LCD (liquid crystal display) light valve assembly and U.S. Pat. No. 4,371,892 describes an exemplary light valve assembly using a PLZT (lanthanum doped lead zirconate titanate) panel. The PLZT kinds of light valve writing devices require individual address electrodes and drive circuitry for each picture element (pixel) of the array, so high resolution and rapid operation also are problems regarding these devices. U.S. Pat. Nos. 4,374,397; 4,375,648; 4,377,753 and 4,805,012 describe systems for interlacing the successive pixel actuations of a light valve array within a single line segment to enhance image resolution on that line and to reduce the complexity of the address and drive electronics. However, these systems write across the transverse width (x-direction) of a strip moving longitudinally (in the y-direction) and are not designed to perform edge data writing on a rapidly moving strip. Active matrix LCD panels using thin film transistor address systems are available and provide high resolution and contrast; however, the liquid crystal material requires a relatively long period (e.g. about 0.050 seconds) to completely reorient. This has motivated against use for printing on rapidly moving strips such as in film spoolers.